The project file enables you to create multiple boards in one project and share schematics across these boards (if you need/want to). A Board refers to a single PCB so in theory you can have multiple PCBs managed by one project. A schematic represents the drawing canvas, it can consist of multiple sheets and also include hierarchy with schematics below the hierarchy. Hierarchical blocks can be instantiated multiple times to replicate design data etc.

There is no 'version' management capability built into the tools though you might work out a scheme to achieve what you want to do though I would suggest you read the documentation before doing so.